This invention concerns displacement transducers and more particularly the LVDT (linear variable differential transformer) type transducers in which a ferromagnetic core element is slidably disposed within a bore formed in a transformer housing, the transformer housing mounting a pair of pickup coils and a power coil which serve to generate a linear output electrical signal in correspondence with the position of the core element in the transformer bore.
Such transducers are widely used in industrial gaging applications in which workpieces are gaged by being disposed with a gaging fixture, with a probe shaft having a probe contact element caused to move outwardly into contact with the workpiece, the electrical signal corresponding to core displacement generating a gaging signal corresponding to a particular dimension of the workpiece.
In automated setups, the probe is caused to be actuated by various arrangements such as to automatically be displaced into contact with the workpiece. Generally, such arrangements include a mechanism external to the LVDT with the actuation components exposed. This creates a gaging setup vulnerable to damage and in industrial plants this is a considerable disadvantage.
Also, the cost of the overall gaging setup is expensive due to the need to assemble the LVDT assembly into the actuation mechanism.
Self-contained actuation arrangements have heretofore been attempted. For the most part, these have consisted of fluid pressure cylinder arrangements located on the backside of the LVDT or other transducer pushing the core and probe shaft into engagement with the workpiece. This backside location precludes the use of standardized electrical connections to the LVDT which normally are supplied with a connector on the rear face designed to mate with standard electrical connectors.
In addition, such designs which have heretofore been provided have been relatively delicate and of a limited short stroke capacity. Many of the designs rely on a fluid actuation of the core element itself which limits the operating characteristics of the actuating to the dimensions of the transformer housing bore and core element.
It is also important in such industrial applications that the actuation arrangement be operated by easily achievable air pressure. If the area under pressure is large, a too-harsh action of the actuator arrangement will result. Whereas, if the air pressure is attempted to be lowered, relatively costly low pressure regulators must be relied on which increase the expense of the gaging setup.
LVDT transducers are generally more costly with increasing gaging range. On the other hand, the range in which the actual gaging needs to be done is relatively limited in comparison to the range of motion of the probe in reaching the surface which is to be gaged. It therefore would be desirable to be able to use relatively short range LVDT transducers in such probe assemblies which could accommodate pretravel (or overtravel) of the probe relative the gaging range of motion of the probe.
In some designs, the mounting of extensions to the LVDT can cause side loadings to be imposed on the LVDT core, and thus to the interior of the LVDT core increasing wear and friction during gaging stroking.
Accordingly, it is an object of the present invention to provide a displacement transducer integrated with an actuator arrangement which is rugged in construction.
It is a further object of the present invention to provide such a combination which does not require modification of the rear face portion of commercially available standard LVDT units, such as to enable standard electrical connectors to be employed therewith.
It is yet another object of the present invention to provide such an arrangement in which the fluid pressure actuation is not achieved by means of the components of the LVDT transducer.
It is still a further object of the present invention to provide a probe assembly utilizing a relatively short range transducer in conjunction with an extended range probe motion.
It is also an object of the present invention to provide a LVDT probe assembly in which side loadings are not transmitted into the LVDT core element.